I would've liked to put this in the other advanced techniques thread but since it's locked I'll put it here.
This is especially useful for longer samples and sounds placed near the end of a pattern. You may notice notes that overlap the pattern end, and this can be disireable at times while other times like going into an all drum part of the track for example can ruin a good break.
For those parts when you need to stop the sound place a note directly before the place you want the sound to stop and in the note edit screen turn that note down until you can no loger hear it.
Since sounds are stopped upon retriggering, this will cut the sound exactly where you want it to end.
This also works well in the middle of a pattern with longer sounds like strings etc, when you need a shorter note.
Give it a try and post some examples!!